Electro-optical modulators (e.g. in the form of Mach-Zehnder modulators) are used in particular for high-bit-rate electro-optical light modulation, for instance for bit rates of between 10 and 100 Gbit/s. Known Mach-Zehnder modulators are often designed and operated according to the serial push-pull principle, as described e.g. in the publication “High-Speed III-V Semiconductor Intensity Modulators”, R. G. Walker, IEEE J. Quantum Electronics Vol. 27, No. 3 (1991) 654-667. In particular, such modulators comprise capacitances to which an RF voltage can be applied via electrodes and which are coupled to one another via an electrically conductive region. The capacitances are respectively assigned to an optical waveguide of the modulator, wherein the RF voltage can act on the optical waveguides via the capacitances. In this way, the RF voltage can influence the phase of an optical wave guided into the waveguide.
A division of the RF voltage in equal halves, said division also being dynamically effective, is desirable for an entirely satisfactory function of the modulator (in particular in order to realize an amplitude modulation as far as possible without chirp of the optical phase), for which reason the capacitances assigned to the modulator electrodes are chosen in particular with identical magnitude. The RF voltage is fed in e.g. asymmetrically (“single-ended”), i.e. one of the electrodes is at ground potential, while the RF signal is fed into the other electrode. Furthermore, a DC voltage (bias voltage) is applied to the electrodes in order to be able to set an operating point of the modulator. The bias voltage is applied in particular via a feed line to the electrically conductive region via which the capacitances of the modulator are coupled to one another. One example of such a modulator is disclosed in the article “High performance InP-based Mach-Zehnder modulators for 10 to 100 Gb/s optical fiber transmission systems”, K.-O. Velthaus et al., IPRM 2011, paper Th-9.2.1.
Upon a rectangular RF voltage being applied to the signal-carrying modulator electrode, the phase of an optical wave propagating in the optical waveguides of such asymmetrically operated modulators often has an undesirably slow, transient switching edge profile, which is attributed e.g. to charge reversal—causing lingering ringing on the RF voltage pulse edges—of the connected capacitances of the modulator and the feed line for feeding in the bias voltage. This transient phase profile is associated with chirp of the optical modulator signal, which can adversely affect the bandwidth of the modulator. In particular, optical chirp disturbs the operation of arrangements which comprise a plurality of interconnected modulators, e.g. so-called IQ modulators.